SHORT STORY: Pick something of value, make bets on the future value of "something", add contract & you have a derivative.
Banks make massive profits on derivatives, and when the bubble bursts chances are the tax payer will end up with the bill.
This visualizes the total coverage for derivatives (notional). Similar to insurance company's total coverage for all cars.

LONG STORY: A derivative is a legal bet (contract) that derives its value from another asset, such as the future or current value of oil, government bonds or anything else. Ex- A derivative buys you the option (but not obligation) to buy oil in 6 months for today's price/any agreed price, hoping that oil will cost more in future. (I'll bet you it'll cost more in 6 months). Derivative can also be used as insurance, betting that a loan will or won't default before a given date. So its a big betting system, like a Casino, but instead of betting on cards and roulette, you bet on future values and performance of practically anything that holds value. The system is not regulated what-so-ever, and you can buy a derivative on an existing derivative.
Most large banks try to prevent smaller investors from gaining access to the derivative market on the basis of there being too much risk. Deriv. market has blown a galactic bubble, just like the real estate bubble or stock market bubble (that's going on right now). Since there is literally no economist in the world that knows exactly how the derivative money flows or how the system works, while derivatives are traded in microseconds by computers, we really don't know what will trigger the crash, or when it will happen, but considering the global financial crisis this system is in for tough times, that will be catastrophic for the world financial system since the 9 largest banks shown below hold a total of $228.72 trillion in Derivatives - Approximately 3 times the entire world economy. No government in world has money for this bailout. Lets take a look at what banks have the biggest Derivative Exposures and what scandals they've been lately involved in. Derivative Data Source: ZeroHedge.

One Hundred Dollars

$100 - Most counterfeited money denomination in the world.
Keeps the world moving.

Ten Thousand Dollars

$10,000 - Enough for a great vacation or to buy a used car.
Approximately one year of work for the average human on earth.

100 Million Dollars

$100,000,000 - Plenty to go around for
everyone. Fits nicely on an ISO / Military
standard sized pallet.

$1 Million is the cash square on the floor.

1 Billion Dollars

$1,000,000,000 - This is how a billion dollars looks like.
10 pallets of $100 bills.

1 Trillion Dollars

$1,000,000,000,000 - When they throw around the word "Trillion" like it is nothing, this is the reality of $1 trillion dollars. The square of pallets to the right is $10 billion dollars. 100x that and you have the tower of $1 trillion that is 465 feet tall (142 meters).

$2 Billion on Truck

Bank of New York Mellon

BNY has a derivative exposure of $1.375 Trillion dollars.
Considered a too big to fail (TBTF) bank. It is currently facing (among others) lawsuits fraud and contract breach suits by a Los Angeles pension fund and New York pension funds, where BNY Mellon allegedly overcharged the funds on many millions of dollars and concealed it.

State Street Financial

State Street has a derivative exposure of $1.390 Trillion dollars.
Too big to fail (TBTF) bank. It has been charged by California Attorney General (among other) lawsuits for massive fraud on California's CalPERS and CalSTRS pension funds - similar to BNY (above).

Morgan Stanley

Morgan Stanley has a derivative exposure of $1.722 Trilion dollars.
Its a too big to fail (TBTF) bank. It recently settled a lawsuit for over-paying its employees while accepting the
tax payer funded bailout. Vice Chairman of Morgan Stanley had a license plate that said "2BG2FAIL" on his Porsche Cayenne Turbo. All this while $250 million of bailout money ended up in the hands of Waterfall TALF Opportunity, run by the Morgan Stanley's owners' wives-- Marry a banker for a $250M tax-payer cash injection.
The bank also got a SECRET $2.041 Trillion bailout from the Federal Reserve during the crisis, beyond the tax payer bailout.

Note the little man standing in front of white house. The little worm next to lastfootball field is a truck with $2 billion dollars.
There is no government in the world that has this kind of money. This is roughly 3 times the entire world economy. The unregulated market presents a massive financial risk. The corruption and immorality of the banks makes the situation worse.

If you don't want to bank with these banks, but want to have access to free ATM's anywhere-- most Credit Unions in USA are in the CO-OP ATM network, where all ATM's are free to any COOP CU member and most support depositing checks. The Credit Unions are like banks, but invest all their profits to give members lower rates and better service. They don't have shareholders to worry about or have derivatives to purchase and sell.

Keep an eye out in the news for "derivative crisis", as the crisis is inevitable with current falling value of most real assets.
Derivative Data Source: ZeroHedge